Electric motors use electrical energy to produce mechanical energy, very typically through the interaction of magnetic fields and current-carrying conductors. The conversion of electrical energy into mechanical energy by electromagnetic means was first demonstrated by the British scientist Michael Faraday in 1821 and later quantified by the work of Hendrik Lorentz.
In a traditional electric motor, a central core of tightly wrapped current carrying material creates magnetic poles (known as the rotor) spins or rotates at high speed between the fixed poles of a magnet (known as the stator) when an electric current is applied. The central core is typically coupled to a shaft which will also rotate with the rotor. The shaft may then be used to drive gears and wheels in a rotary machine and/or convert rotational motion into motion in a straight line.
Generators are usually based on the principle of electromagnetic induction, which was discovered by Michael Faraday in 1831. Faraday discovered that when an electrical conducting material (such as copper) is moved through a magnetic field (or vice versa), an electric current will begin to flow through that material. This electromagnetic effect induces voltage or electric current into the moving conductors.
Current power generation devices such as rotary alternator/generators and linear alternators rely on Faraday's discovery to produce power. In fact, rotary generators are essentially very large quantities of wire spinning around the inside of very large magnets. In this situation, the coils of wire are called the armature because they are moving with respect to the stationary magnets (which are called the stators). Typically, the moving component is called the armature and the stationary components are called the stator or stators.
In most conventional motors, both linear and rotating, enough power of the proper polarity must be pulsed at the right time to supply an opposing (or attracting) force at each pole segment to produce a particular torque. In conventional motors at any given instant only a portion of the coil pole pieces is actively supplying torque.
With conventional motors, a pulsed electrical current of sufficient magnitude must be applied to produce a given torque/horsepower. Horsepower output and efficiency then is a function of design, electrical input power plus losses.
With conventional generators, an electrical current is produced when the rotor is rotated. The power generated is a function of flux strength, conductor size, number of pole pieces and speed in RPM. However output is a sinusoidal output which inherently has losses similar to that of conventional electric motors.
Specifically, the pulsed time varying magnetic fields produces undesired effects and losses, i.e. iron hysteresis losses, counter-EMF, inductive kickback, eddy currents, inrush currents, torque ripple, heat losses, cogging, brush losses, high wear in brushed designs, commutation losses and magnetic buffeting of permanent magnets. In many instances, complex controllers are used in place of mechanical commutation to address some of these effects.
Additionally, in motors or generators, some form of energy drives the rotation and/or movement of the rotor. As energy becomes more scarce and expensive, what is needed are more efficient motors and generators to reduce energy consumption, and hence costs.